A piston of the above kind is described in, for example, U.S. Pat. No. 4,581,985 and the corresponding French published patent application No. FR 2 523 244A. In those documents, the piston includes, firstly a member in the form of a cup member having a base portion and adapted to be engaged in a cylinder of the hydraulic brake, and secondly an insulating core member of heat insulating material, which is engaged at least partly in the cup member and which projects from the latter, the core member being fastened to the cup member by fastening means with a force fit. The fastening means are localised, and affect only part of the side walls of the core and cup members.
Such an arrangement complicates assembly and manufacture. In order to overcome this disadvantage, the piston itself may be assembled by bolting it to the insulating body in the manner described in French published patent application No. FR 2 005 742A. However, an arrangement of this kind is equally unsatisfactory, because it requires the thickness of the base portion of the cup member to be increased.